[mjgrantham]

I'm not familiar with rear heat since my Venture doesn't have it. But it definitely sounds like something is letting air into the system and you need to find it. Has the coolant level dropped in the overflow tank that you can see? Do you see or hear any coolant leaks? If not, try this: remove the front spark plugs and see if one is coated crusty white. This would indicate coolant being burned in that cylinder, hence a head gasket leak. If the front three look good then you could try getting to the rear plugs (arghh). I had the same symptoms you described and confirmed a head gasket failure when I found the #1 plug to be covered in coolant by-product. I also found a cooling system pressure tester to be INVALUABLE, rented free from Advance Auto Parts (available at others too). Just hook up to radiator filler neck (engine cold), pump up to max system pressure and watch the guage. If it drops, even very slowly, it's telling you there is a leak. Any external leak will be obvious, as you will hear it spraying out fluid and air. You can touch around the engine and get down close to look without getting burned - nice! If you don't see or hear anything leaking and the guage drops, then the leak is internal, either head gasket or intake manifold gasket. An intake manifold gasket leaking internally will seep coolant into the oil and cause engine damage if allowed to go on.

Hopefully you just had an unusual volume of air to bleed out but it looks as if you may need to pursue a few other avenues to fix this. Don't hesitate to ask more questions if you need further help.

Peace.

Mike